Films of metals and metal oxides, particularly the heavier elements of Group VIII, are becoming important for a variety of electronic and electrochemical applications. This is at least because many of the Group VIII metal films are generally unreactive, resistant to diffusion of oxygen and silicon, and are good conductors. Oxides of certain of these metals also possess these properties, although perhaps to a different extent.
Thus, films of Group VIII metals and metal oxides, particularly the second and third row metals (e.g., Ru, Os, Rh, Ir, Pd, and Pt) have suitable properties for a variety of uses in integrated circuits. For example, they can be used in integrated circuits for electrical contacts. They are particularly suitable for use as the plate (i.e., electrode) itself in capacitors. In addition, Group VIII metals are useful in catalysts.
Platinum is one of the candidates for use as an electrode for high dielectric capacitors. Capacitors are the basic charge storage devices in random access memory devices, such as dynamic random access memory (DRAM) devices, static random access memory (SRAM) devices, and now ferroelectric memory (FE RAM) devices. They consist of two conductors, such as parallel metal or polysilicon plates, which act as the electrodes (i.e., the storage node electrode and the cell plate capacitor electrode), insulated from each other by a dielectric material (a ferroelectric dielectric material for FE RAMs). It is important for device integrity that oxygen and/or silicon not diffuse into or out of the dielectric material. This is particularly true for ferroelectric RAMs because the stoichiometry and purity of the ferroelectric material greatly affect charge storage and fatigue properties. Also, oxidation of the underlying silicon will result in decreased series capacitance, thus degrading the cell capacitor.
In order to function well in a bottom electrode, the electrode film or film stack must be able to withstand the high temperature anneals required to recrystallize the dielectric layer. As stated above, platinum is one of the candidates for use as an electrode material for high dielectric capacitors. Platinum, alone, however, in the form of films deposited by chemical vapor deposition techniques can be unstable when annealed at temperatures 650° C. and above. For example, as shown in FIG. 1, a platinum layer can form islands during the anneal process, which suggests high mobility of platinum at temperatures far below its melting temperature. One solution is to combine (e.g., alloy) the platinum with rhodium to enhance the barrier properties and stability of the layer; however, rhodium precursors can be very expensive.
Thus, there is a continuing need for methods and materials for the deposition of stable platinum-containing films, particularly those that can be subjected to relatively high annealing temperatures.